Conventionally, as this type of tube coupling joints, those made of a resin, which is typified by a fluorocarbon resin, are well known, and they are divided into two broad general categories; i.e., the “inner ring type” as shown in FIG. 19, which inserts a ring into the inside of the tube, and the “flare type” as shown in FIG. 20, which flares the tube.
As the tube coupling joint of inner ring type, that as disclosed in Patent Document 1 is known, and as the tube coupling joint of flare type, that as disclosed in Patent Document 2 is known. The tube coupling joints of these types have their inherent advantages and disadvantages.
Advantages of the inner ring type include that, once the ring is inserted into the tube, processing of the tube is completed, thus excellent assemblability being assured, and that, when the tube is subjected to a tensile load, the ring serves to prevent the tube from coming off, thus a high tensile strength being provided.
The advantages of the flare type include that the coupling portion of the tube and that of the joint main body are pressure-contacted with each other by means of the cap nut, resulting in no gap being produced, thereby the possibility of penetration of the fluid being low, and that, unless the tube is positively flared, the tube cannot be mounted to the joint main body, whereby a mistake leading to an accident can be prevented.